Sounds like way too much fuel. try new plugs, or at least look at ALL 8 to see what they look like and if they all look alike. I'd also recomend doing a compression test on all 8 cyls, and double check the base timing.

Have you another carb to try? I would suspect the carb is either dirty or way out of what. Any idea what you have for a cam in there? Compression ratio?

What car have you got it in, auto or manual, and what are you using for headers/exhaust?